On the KGPE-D16 with commit 4.5-566-geb9c639 there two IRQ errors that appear soon after boot and use of a SCSI tape device, which appear to cause a reduced tape speed. The tape library is connected via SCSI to a Symbios Logic 53c895 adapter, via an ASMedia ASM1083/1085 PCIe to PCI Bridge.

At first read speeds are about 60 MB/s, then the system may hang for a few seconds and IRQ errors appear on the screen. At this time, iotop shows that the speed reduces 10 MB/s. If not using microcode, the speed is reduced to 100 KB/s. This may also be the case when using the 20160907 libreboot config to build a recent upstream coreboot, with or without microcode, seemingly caused by use of static option tables.

I have attempted to boot with the irqpoll option, but this did not resolve the issue. I am using iommu=soft, as this is the only way that the tape device is being recognized by the system. Otherwise, dmesg logged the following: